1986 Bronco II EB 4wd 2.9 gas - warmed up dies no run for 20+ minutes

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Motech

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there are no CEL's installed previous 1988 as owners in CA had to find out to pass smog tests.

Almost.

Check Engine lights were not required to pass a California smog check inspection on most light trucks until 1990, but most every domestic EFI (and many carbureted) light trucks had them.
 

jdabnabe

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I've been chasing the "heat up and won't run" demon aka curse of the 2.9 since March 2020 on my 1986 EB 4wd B2 2.9 gas I'm the 2nd owner and we know this problem never existed until 3/2020. All these have been replaced as a result -> Plugs, Wires, Alternator, Battery & Cables, Coil, Condenser, Ignition switch, IAC, 2 new TPS, 5 new in tank pumps, in-tank pump plug, 2 new hp rail pumps, distributor, relays, 9 ECM's, 3 or 4 harness plugs, inertia switch, inertia plug, fuel filter, fuel regulator, MAP sensor, (o2, air temp, engine temp sensors). allegedly all ground connections cleaned up and passed voltage drop tests (no details received)

The problem first was that I watched a mechanic hook up a pressure gauge to the fuel line and while vehicle was running fine it was close to 40psi. In 18 minutes as predicted it coughed and sputtered, died and won’t restart as expected, as it coughed the fuel psi was 5-10 and he said there’s the issue a new rail pump needed. That was not the cure as 2 more fuel pumps later it still does this same thing – idle for 20-40 minutes sputters and dies won’t start and run properly for 30+ minutes. Sometimes you can just drive it for 60+ minutes and notice it might buck when you step on the gas or it may die at a red light and I will be stuck for 30 minutes. The other day i idled it in the driveway for 60 minutes and it was fine, next day drove it for 70 minutes idled in the driveway for 15 and it died.

Lots of talk always about the issue of the TFI overheating on the distributor, but I look at my records and I have never had anything near this issue before. I see the 1st TFI was replaced at 9 years 34k miles, the second lasted 12 years 94k more miles, the 3rd lasted 11 years 77k miles. Reinstalled a new one each time no issue. I don’t see why a TFI should be relocated.

FYI - I'm not a mechanic, i'm the researcher and yes i can change the plug wires and coil and simple things - but i have paid 3 shops one is a supposedly classic auto shop and after 1 year they said they give up. Another classic auto shop said no i won't work on that issue. This is a family heirloom that i drove from 96-2016, i got it with 34k and it now has 208k. All along trying to fix this running issue i have lots of other new parts and plan to rebuild motor/tran and possibly repaint. Who in Tampa Bay area can fix this? Any direction appreciated. Thank you. Completly frustrated and about heartbroke and wallet broke.
I had a very similar issue with my Bronco. I had done pretty much everything you did and still had this stumble/lack of power. I had all new fuel tank, pump, sending unit, fuel lines, cap, rotor, wires, plugs, coil, TPS, O2 sensor and exhaust.

My problem was rust in the tank completely clogging the fuel filter and fuel strainer on the pump. I went through 4 sets before I figured out it was rust falling from the top of the brand new tank. I thought it would clear up with a few fuel filter/strainer changes. It didn’t. I had Advance warranty out the tank and bought the POR15 fuel tank coating. I dropped both off at my painter and $110 dollars later ($50 for the POR15, $60 for the labor) I have no more problems with lack of power.

I only figured it out because I had installed a permanent fuel pressure gauge on the rail and at idle it was hovering right at 32PSI. Right at the bottom of the acceptability level. It would only do it after about 20 minutes of driving and when I would get home to try and trouble shoot it it wouldn’t do it again. Finally it did it right before I got home and parked the truck, popped the hood, romped the throttle and saw the gauge go to zero. I cut the filter open and it was completely clogged with rust and “sand”. I popped the top off of the tank and saw the rust and “sand” on the bottom of the tank. So it might have been bad fuel but I had only gotten a tank of non-ethanol from my regular supplier, numerous from Costco, one from a Shell and one from another station.

Anyway, I hope this helps.
 

goodO1boydws

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It sounds as if you've tried a ----load of other things, try this:

Run the engine until it dies.
Position a bag of ice so it surrounds the ignition control module, on the distributor.
With the icebag still in place, try to start the engine every 2 minutes.
See if it restarts in a shorter amount of time than its been taking.
 

L\Bronco

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I really did get to do the PIP test a couple minutes ago. Here are lots more details:
I am wondering why throughout the 3 years consistantly run a little longer every few months. It first would mostly be 18 minutes then a year later up to 30 minutes. This past 2 weeks, 2 times it now runs for 80 minutes before the issue. The last mod increased it from 30 minutes to 80 minutes. Here are lots of details:

In July I idled it for 30 minutes until it died then I went to remove the ECM and it was so hot you could not touch it without getting burned. I let it cool and left it alone was not able to work with it until a couple weeks ago when the mech reproduced the problem at his shop he found the 2 grnd wires next to the ECM, 1 insulated 1 not insulated (he knew what they are for) was hanging by 3 strands, surprised I did not catch that as many times I removed ECM, but he fixed that connection up really good. I had not previously told him about the heated up ECM. Now we run 80 minutes and when it dies the ECM is only as expected "very warm". I had also noticed in July after 20 minutes there is a sound in the dash that could be the sound of the HP pump but only after 20 minutes. At time of issue the sound changes from a hum to a rougher hum. I still wonder if the LP pump burns out because of bad amperage from bad wire and the HP pump can actually run the 2.9 although it's not supposed to, for as long as it can. The other day I did the pin 6 ground to turn on the fuel pumps. I can easily hear the HP pump but I can not tell at all if the LP pump is on. I even climbed underneath and put my hand ontop of the send unit and could not feel the slightiest vibe. The issue just happened for my second time in 2 weeks after idling for 80 minutes.

I now have a video of dash as it looks when cranking after the die out. I can hear the HP pump prime but no start. I am also puzzled a litte more about the lights. Why does the parking brake light come on during crank? The P brake light comes on as supposed to when park brake is on. Also, the Check Engine bulb is not present, i have some photos of last year when i had the dash apart for umteenth time for various reasons, but i was changing over to LEDs and there is a photo documenting what bulbs are present and only the ones i replaced. I am going to have to upload the PIP test video to an external link. B2 dashview lights for heatup and won't run issue-->
The symptom when there is no fuel coming from the lp pump is exactly what yours is doing.
The best test would be to recreate the failure, and remove the inlet line from the hp pump and put it into a container, (it comes from the lp pump) then run the pumps with the jumper as you did before. You should get a quart in 30 to 60 sec.
Note: if the hp pump loses its prime it will get very loud.
Hope that helps.
Cheers
 

johnnyreb

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I've been chasing the "heat up and won't run" demon aka curse of the 2.9 since March 2020 on my 1986 EB 4wd B2 2.9 gas I'm the 2nd owner and we know this problem never existed until 3/2020. All these have been replaced as a result -> Plugs, Wires, Alternator, Battery & Cables, Coil, Condenser, Ignition switch, IAC, 2 new TPS, 5 new in tank pumps, in-tank pump plug, 2 new hp rail pumps, distributor, relays, 9 ECM's, 3 or 4 harness plugs, inertia switch, inertia plug, fuel filter, fuel regulator, MAP sensor, (o2, air temp, engine temp sensors). allegedly all ground connections cleaned up and passed voltage drop tests (no details received)

The problem first was that I watched a mechanic hook up a pressure gauge to the fuel line and while vehicle was running fine it was close to 40psi. In 18 minutes as predicted it coughed and sputtered, died and won’t restart as expected, as it coughed the fuel psi was 5-10 and he said there’s the issue a new rail pump needed. That was not the cure as 2 more fuel pumps later it still does this same thing – idle for 20-40 minutes sputters and dies won’t start and run properly for 30+ minutes. Sometimes you can just drive it for 60+ minutes and notice it might buck when you step on the gas or it may die at a red light and I will be stuck for 30 minutes. The other day i idled it in the driveway for 60 minutes and it was fine, next day drove it for 70 minutes idled in the driveway for 15 and it died.

Lots of talk always about the issue of the TFI overheating on the distributor, but I look at my records and I have never had anything near this issue before. I see the 1st TFI was replaced at 9 years 34k miles, the second lasted 12 years 94k more miles, the 3rd lasted 11 years 77k miles. Reinstalled a new one each time no issue. I don’t see why a TFI should be relocated.

FYI - I'm not a mechanic, i'm the researcher and yes i can change the plug wires and coil and simple things - but i have paid 3 shops one is a supposedly classic auto shop and after 1 year they said they give up. Another classic auto shop said no i won't work on that issue. This is a family heirloom that i drove from 96-2016, i got it with 34k and it now has 208k. All along trying to fix this running issue i have lots of other new parts and plan to rebuild motor/tran and possibly repaint. Who in Tampa Bay area can fix this? Any direction appreciated. Thank you. Completly frustrated and about heartbroke and wallet broke.
I noticed no one THOUGHT it might be the gas. Their is a bottle of stuff called Star Thron . You pour a little in tthe tank and I have found its the best stuff I have used. Better the Seafoam buy a mile. Good luck. A big bottle at Walmart cost $20 or $21 . It is good for 92 gallon of gas.
 
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Tpremru

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Add battery pigtail ground inspect as your number 1
Both battery cables are new all the way to end points. (they look great) Including the 2 smaller wires on the ground (pigtail - looks great) - 1 goes to body just above radiator and the other must be that pin 60. That wire had a quick disconnect that served no purpose other that to provide a spot to get "greened" so that wire is replaced from battery to just past where the quick disconnect was.
 
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Tpremru

Tpremru

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The symptom when there is no fuel coming from the lp pump is exactly what yours is doing.
The best test would be to recreate the failure, and remove the inlet line from the hp pump and put it into a container, (it comes from the lp pump) then run the pumps with the jumper as you did before. You should get a quart in 30 to 60 sec.
Note: if the hp pump loses its prime it will get very loud.
Hope that helps.
Cheers
Thank you, when you say "The symptom when there is no fuel coming from the lp pump is exactly what yours is doing." ---> this in my mind is starting to add up to bad wire feed or ground to Lpump, causes new Lpump to burn out in a matter of a couple hours or less use. I say this because last year after i put in the second Lpump i took it to local classic shop, they put in Lpump and said "you are good to go all tested". When they test it they did drive it quite a bit like maybe upto 50 miles. I brought it right back and said not fixed. They told me they dropped the tank put 12v to the Lpump and nothing, i said "you checked the wires - it's a new pigtail plug on there?" they said "no voltage drop at that wire". They installed another new Lpump and we got the exact repeat where they put 12v to Lpump and got nothing. I told them i will buy a NOS Lpump and that's where i am now but suspicious it went bad last year soon after they installed it. I'm now comtemplating to see if i can disconnect front pump & do the jumper test to stephoscope on the Lpump if this is possible. Otherwise i will have to wait until next week or the next at the shop and also do the "flow" test of Lpump. As yet another idea to run seperate wires to Lpump and see if issue occurs. I wonder if i have to replace wires and both pumps?
 
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Tpremru

Tpremru

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Almost.

Check Engine lights were not required to pass a California smog check inspection on most light trucks until 1990, but most every domestic EFI (and many carbureted) light trucks had them.
I guess that video i posted of crank and no start issue is no help?
 
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Tpremru

Tpremru

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I had a very similar issue with my Bronco. I had done pretty much everything you did and still had this stumble/lack of power. I had all new fuel tank, pump, sending unit, fuel lines, cap, rotor, wires, plugs, coil, TPS, O2 sensor and exhaust.

My problem was rust in the tank completely clogging the fuel filter and fuel strainer on the pump. I went through 4 sets before I figured out it was rust falling from the top of the brand new tank. I thought it would clear up with a few fuel filter/strainer changes. It didn’t. I had Advance warranty out the tank and bought the POR15 fuel tank coating. I dropped both off at my painter and $110 dollars later ($50 for the POR15, $60 for the labor) I have no more problems with lack of power.

I only figured it out because I had installed a permanent fuel pressure gauge on the rail and at idle it was hovering right at 32PSI. Right at the bottom of the acceptability level. It would only do it after about 20 minutes of driving and when I would get home to try and trouble shoot it it wouldn’t do it again. Finally it did it right before I got home and parked the truck, popped the hood, romped the throttle and saw the gauge go to zero. I cut the filter open and it was completely clogged with rust and “sand”. I popped the top off of the tank and saw the rust and “sand” on the bottom of the tank. So it might have been bad fuel but I had only gotten a tank of non-ethanol from my regular supplier, numerous from Costco, one from a Shell and one from another station.

Anyway, I hope this helps.
Thanks jdabnabe. I know we replaced the in line filter in the canister and also the sock on the Lpump is always new (5 Lpumps now) When mine gets to a certain temp it will not run or start for 10+ minutes, better to cool it for 30 minutes to be able to get home, maybe.
 
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Tpremru

Tpremru

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It sounds as if you've tried a ----load of other things, try this:

Run the engine until it dies.
Position a bag of ice so it surrounds the ignition control module, on the distributor.
With the icebag still in place, try to start the engine every 2 minutes.
See if it restarts in a shorter amount of time than its been taking.
Would you believe i did that test in June! I did it 3 times, once i thought the bag of ice on the ICM made a difference so i did it 3 times and could not find any difference. The first time i thought that was it....only to change the ICM again with no difference. Thanks though!
 

goodO1boydws

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Say, yu didn't answer if teh spark goes away when the engine dies. (Well, the ice bag is always worth trying-with as many millions of these distributor mounted ICM failures as Fords have had.)

You DID add the proper grease when replacing the ICU I hope. Some people skip that step.)

It certainly sounds as though something is just barely making contact and that its temperature rise which is opening the circuit. It could even be a wire that is frayed and has some of its insulation missing and is heating up from current load, and only movng and making contact with a ground or another wire when its hot.

That 20 minute run interval then dying is exactly what was happening with the connector plug on my 1986 B2's fuel shut off switch under the front carpet.
At first, the engine would die at about 20 minutes and it got progressively shorter. (At least near the end I could easily WALK home.) The connector was half melted when I found it-no telling how long it had been doing that (weeks, months, years?) before one of its internal contacts was out of position just enough to be opening up when heated by the current running throughj= it.

Another time (on a different Ford, but one with the identical ignition system) it was the throttle position sensor preventing RESTARTING-with a 20 minute cooling off period. It would run fine (EVEN FOR 3 HOURS) as as long as the the car was moving enough to generate sufficient airflow through the engine compartment to restart it. If I shut it off for more than about 20-30 seconds I was in for a 20 minute wait.

Say, did you answer earlier in the thread if the spark goes away when the engine dies and it can't be restarted?
 
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Tpremru

Tpremru

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Say, yu didn't answer if teh spark goes away when the engine dies. (Well, the ice bag is always worth trying-with as many millions of these distributor mounted ICM failures as Fords have had.)

You DID add the proper grease when replacing the ICU I hope. Some people skip that step.)

It certainly sounds as though something is just barely making contact and that its temperature rise which is opening the circuit. It could even be a wire that is frayed and has some of its insulation missing and is heating up from current load, and only movng and making contact with a ground or another wire when its hot.

That 20 minute run interval then dying is exactly what was happening with the connector plug on my 1986 B2's fuel shut off switch under the front carpet.
At first, the engine would die at about 20 minutes and it got progressively shorter. (At least near the end I could easily WALK home.) The connector was half melted when I found it-no telling how long it had been doing that (weeks, months, years?) before one of its internal contacts was out of position just enough to be opening up when heated by the current running throughj= it.

Another time (on a different Ford, but one with the identical ignition system) it was the throttle position sensor preventing RESTARTING-with a 20 minute cooling off period. It would run fine (EVEN FOR 3 HOURS) as as long as the the car was moving enough to generate sufficient airflow through the engine compartment to restart it. If I shut it off for more than about 20-30 seconds I was in for a 20 minute wait.

Say, did you answer earlier in the thread if the spark goes away when the engine dies and it can't be restarted?
Thanks god01boydws for you input!

I made sure they had the proper grease with the new ICM 3 times now!

I have not tested for that spark going away yet....that probably will have to wait for a week or 2 when i get it back to the shop, however, it seems as spark is still there because when it dies and you try to restart - it does cough and sputter (see the video in an earlier post above), you can hear the HP prime, which i have even tried on/off 4 or 5 times to see if any difference.

Mine has progressively run longer from 20 then 30 now 80 minutes. The connector plug to the inertia switch is new, i personally took out the inertia switch and took it apart and inspected it 12/2020 - looks so new/clean no carbon tracing - i put a meter on it and tested it 9 ways to Sunday and it works great.

11/2021 i changed the TPS (Motorcraft) it definitly fixed my idling. I was distressed to hear when i picked it up from shop they replaced it about 6 months ago with a probably low line Napa. So PO'd i did not pay for that...they said they adjusted it...i'm still wondering how can you adjust that TPS? A couple of weeks ago i ordered a new Motorcraft and have that on hand because the idling thing was happening again but i tapped on the TPS and now it works ok. (makes me wonder about that connector even though it looks decent, it has not been replaced) That reminds me that earlier this year i remember pulling out of the driveway and it stalled as i pulled out of driveway thru the dip type gutter. It would not readily restart. And that made me think of a bad wire, but where? It has not done that since that one time.

When i get it to the shop next week or 2, i will definitly have them check the Lpump to see if it is even coming on and also a flow check.
 

johnnyreb

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Thanks god01boydws for you input!

I made sure they had the proper grease with the new ICM 3 times now!

I have not tested for that spark going away yet....that probably will have to wait for a week or 2 when i get it back to the shop, however, it seems as spark is still there because when it dies and you try to restart - it does cough and sputter (see the video in an earlier post above), you can hear the HP prime, which i have even tried on/off 4 or 5 times to see if any difference.

Mine has progressively run longer from 20 then 30 now 80 minutes. The connector plug to the inertia switch is new, i personally took out the inertia switch and took it apart and inspected it 12/2020 - looks so new/clean no carbon tracing - i put a meter on it and tested it 9 ways to Sunday and it works great.

11/2021 i changed the TPS (Motorcraft) it definitly fixed my idling. I was distressed to hear when i picked it up from shop they replaced it about 6 months ago with a probably low line Napa. So PO'd i did not pay for that...they said they adjusted it...i'm still wondering how can you adjust that TPS? A couple of weeks ago i ordered a new Motorcraft and have that on hand because the idling thing was happening again but i tapped on the TPS and now it works ok. (makes me wonder about that connector even though it looks decent, it has not been replaced) That reminds me that earlier this year i remember pulling out of the driveway and it stalled as i pulled out of driveway thru the dip type gutter. It would not readily restart. And that made me think of a bad wire, but where? It has not done that since that one time.

When i get it to the shop next week or 2, i will definitly have them check the Lpump to see if it is even coming on and also a flow check.
Their is alot of China bootleg parts out their. In reputeable boxes and the work. So you might want have the new parts checked(if you can) Their is alot of junk parts all shine up and it fancy boxes. That ,s not worth anything.
 

goodO1boydws

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11/2021 i changed the TPS (Motorcraft) it definitly fixed my idling. I was distressed to hear when i picked it up from shop they replaced it about 6 months ago with a probably low line Napa. So PO'd i did not pay for that...they said they adjusted it...i'm still wondering how can you adjust that TPS? A couple of weeks ago i ordered a new Motorcraft and have that on hand because the idling thing was happening again but i tapped on the TPS and now it works ok. (makes me wonder about that connector even though it looks decent, it has not been replaced) That reminds me that earlier this year i remember pulling out of the driveway and it stalled as i pulled out of driveway thru the dip type gutter. It would not readily restart. And that made me think of a bad wire, but where?
If it will run for up to 80 minutes now it sounds as though you're very close to having it solved.

If tapping on the TPS made it function properly, perhaps the TPS mounting surface is oxidized and base of the sensor/switch isn't making good electriucal contact. (I don't remember if the TPS's base is metal or not-some are some aren't.) Another thing to try is burnishing the contacts on both the TPS and the pigtail it plugs into-by connecting and disconnecting them several times.

If the plug is oxidized inside and not making good electrical contact with those from the TPS, that could cause or add to the problem. It wouldn't hurt to clean out the connector as the original ones, which usually have thick white grease in them may not have ANY and if there's any green present there, the brass in the contacts has been oxidizing. Even a thin film of oxidation can make for a poor electrical connection. Often simply sliding the connectors together and apart a few times will improve contact, BUT if one of the contacts is BADLY oxidized or has been arcing the metal may be very thin or weak and a few more times connecting it may break the connection entirely.
Luckily there are replacement pigtails available.
Tail light wiring and sockets are especially prone to this "oxidation/erosion" in salt belt areas because of their location, but it can happen in unexpected places too.

Moving on.
On many vehicles the throttle position sensor is mounted with screws or bolts that go through holes in the sensor mounting that are larger than they need to be simply to hold it in place. Some are actually slots rather than round holes. (My wife's Nissan had one with long slots.)
Round hole or slot, there has to be at least enough rotation available to allow SOME adjustment to compensate for manufacturing tolerances and to take up the slack or "dead range" that is almost always present at the beginning of the switch's rotation.

At the beginning of its range of rotation the throttle position sensor/switch will allow some degree of movement before it begins to alter the electrical signal from its "at rest/idle" position.
When the mounting screws/bolts are NOT in place you can usually rotate the switch manually and feel at what point spring tension begins. The IDLE position for the sensor is generally-but not always, at the very beginning of where you start to feel the spring pressure. Depending on how the sensor/switch is mounted say on a metal plate, it may be possible to file the holes/slots wider to allow for more adjustment.

If the "slack" in the TPS's mounting position isn't taken up, and your throttle cable or linkage is adjusted properly, there will be excess pedal movement needed to get the engine's speed off idle. On teh other hand, if the TPS is adjusted too tightly, it will already be signalling the computer that you want to be off idle.

Lastly, hitting that dip and the engine instantly dying also points to a weak connection-IMHO more likely a GROUND connection as the vehicle's body and frame will both flex when that happens, so I'd look there first. Unless you happen to have a battery hanging from its cables.
 
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Tpremru

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Thank you again for your input good01boydws. I am now going to check on the TPS completely. The body and frame grounds main connects are really good if not new or "recently cleaned up". But i agree that at least one time that acted like a bad connection hitting that dip.

I also have this idea that because we removed 3 harness plugs under the master cylinder because of their "greeness" i wondered if there was 1 feed for both fuel pumps that splits in 2 at one of those plugs. Would you know? I think i took pics of what i am describing. And then there is the pic way back by the fuel tank. I'm thinking that if this is true "feed splits into 2" then i will disconnect the HP pump to see if i can at all tell if the back pump runs, before dropping tank etc. thanks
 

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L\Bronco

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Thank you, when you say "The symptom when there is no fuel coming from the lp pump is exactly what yours is doing." ---> this in my mind is starting to add up to bad wire feed or ground to Lpump, causes new Lpump to burn out in a matter of a couple hours or less use. I say this because last year after i put in the second Lpump i took it to local classic shop, they put in Lpump and said "you are good to go all tested". When they test it they did drive it quite a bit like maybe upto 50 miles. I brought it right back and said not fixed. They told me they dropped the tank put 12v to the Lpump and nothing, i said "you checked the wires - it's a new pigtail plug on there?" they said "no voltage drop at that wire". They installed another new Lpump and we got the exact repeat where they put 12v to Lpump and got nothing. I told them i will buy a NOS Lpump and that's where i am now but suspicious it went bad last year soon after they installed it. I'm now comtemplating to see if i can disconnect front pump & do the jumper test to stephoscope on the Lpump if this is possible. Otherwise i will have to wait until next week or the next at the shop and also do the "flow" test of Lpump. As yet another idea to run seperate wires to Lpump and see if issue occurs. I wonder if i have to replace wires and both pumps?
Hey Tpremru:
It sounds like you are going in many directions on this one.
Voltage loss in the harness can cause premature winding failure in a new pump for sure, the most accurate check would be to measure the voltage between the pump feed and ground wires at the lp pump WITH THE PUMP RUNNING!
(That last bit is critical!)
If it is within .5vdc of the battery voltage (while the pump is on) your wires and connections are good.
If not, repeat the measurement between B+ (at the battery) and the positive wire at the lp pump)
Then do the same between ground and Batt - .
Remember, the pump must be running for all measurements.
(Id still look for foreign material in the tank)
Good luck
Cheers
 
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Tpremru

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The first few people were throwing parts at it because it seemed simple and inexpensive to do, not actually blaming them for that but that's how it turns out, i think the first guy was more worried about introducing additional problems which quite possibly it has. Henceforth - many directions.

The other shop said they measured for voltage drop back at the pump but i am thinking they just metered it once not while pump is running and not during or after issue not like you described. Your test sounds like the tank has to be dropped to get to the wire ends at the Lpump and the fuel line disconnected? Thanks.
 

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Thank you again for your input good01boydws. I am now going to check on the TPS completely. The body and frame grounds main connects are really good if not new or "recently cleaned up". But i agree that at least one time that acted like a bad connection hitting that dip.

I also have this idea that because we removed 3 harness plugs under the master cylinder because of their "greeness" i wondered if there was 1 feed for both fuel pumps that splits in 2 at one of those plugs. Would you know? I think i took pics of what i am describing. And then there is the pic way back by the fuel tank. I'm thinking that if this is true "feed splits into 2" then i will disconnect the HP pump to
I can't answer the 1 wire feeding 2 pumps question. But a schematic might.

I suspect that there may be an issue lurking in the second photo, which I take to be the replacement for one of the removed greened connectors under the master cylinder.

Having 5 places where wires are pressure/crimp connected to each other or to a connector within about 3 inches, makes me wonder if one or more of those connections might be less than optimal simply from the strain on them while making the attachments to the connectors in such a confined space. (I've had plenty of wires pull partway out of connectors while crimping them.) And all those extra connections adds places for introducing voltage drop as others have mentioned.

Also, the yellow crimp connector looks to be the type that that isn't sealed from the weather so it will be degrading over time, and the insulation on the brownish wire on the right doesn't look too happy, maybe from being overheated. Does the insulation look any better further back on that one? If not you may need to go back much further to get a better connection. I know its a pain in the ***, but decent soldering and sealing with a weathertight coating such as resin-filled shrink tubing makes better long term electrical connections than crimping in sections of spliced wire does.

Do you remember how the wire itself inside the insulation on those wires looked when you stripped them back to attach the connectors? Sometimes the wire is greened (corroded or oxidized) back several inches from a bad connector before its clean enough to make a good, dependable electrical connection.
 
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Tpremru

Tpremru

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I can't answer the 1 wire feeding 2 pumps question. But a schematic might.
I'm not the one who did the actual stripping and reconnecting but i trust the person doing this was really cautious about the green corrosion which is what started us down that path of the removing 3 plugs fuel realated plugs temporaryily. The crimps were intended to be very temporary as we went to the salvage yard 12/2020 and found another set of same plugs but they were not much better, so i soaked them all in vinegar and baking soda, filed them, sanded them dried them and repeated, whew, with intentions of putting them all back on professionaly as you describe, only after we solve the issue! example of 1 of the greened out plugs attached.
 

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Motech

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The IDLE position for the sensor is generally-but not always, at the very beginning of where you start to feel the spring pressure

This can be misleading as it is simply untrue. All TPS--Ford and everyone else--are installed with some preload so they do not create a closed-throttle dead zone. To believe otherwise will spin a man in diagnostic circles.

I am now going to check on the TPS completely

Don't spin yourself into diagnostic circles.

i wondered if there was 1 feed for both fuel pumps that splits in 2 at one of those plugs.

Indeed, at connector # C161 between inertia switch and fuel pumps, which Ford sayus is located at the LH Fender Apron.


BroncoIIfuelpumpdiagram.png

I'm not the one who did the actual stripping and reconnecting but i trust the person doing this was really cautious about the green corrosion which is what started us down that path of the removing 3 plugs fuel realated plugs temporaryily. The crimps were intended to be very temporary as we went to the salvage yard 12/2020 and found another set of same plugs but they were not much better, so i soaked them all in vinegar and baking soda, filed them, sanded them dried them and repeated, whew, with intentions of putting them all back on professionaly as you describe, only after we solve the issue! example of 1 of the greened out plugs attached.

There is a reason these plugs are obsolete, and no reason to retain their originality. Setting yourself up with new connectors is an excellent upgrade, and an experienced electrical tech should be able to upgrade yours to infallible Weather Pack connectors for the price of a nice dinner for two.


EWP-03K-2T.jpg prd_zm_102.jpg

%2fwww.eastwood.com%2fimages%2f31676infoimage640_1.jpg 42378743425_8d0c439f19_h.jpg
 
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